The present invention relates to facsimile reproduction equipment and in particular to a system for shaping the scanning spot of facsimile transmitting and receiving equipment for optimum reproduction.
Facsimile equipment is used to transmit visual images such as photographs and the like from one location to another. Images reproduced by a facsimile receiver generally exhibit a line or dot structure due to the scanning nature of the electro-optical reproduction process employed. Heretofore, attempts have been made, utilizing recent advances in the fields of electronics, physics and optics to minimize and ideally remove the lines or dots from the reproduction. To this end, facsimile equipment utilizing lasers have been employed with the laser beam passed through a suitable aperture arrangement to produce a generally rectangular scanning spot with a dimension transverse to the scan direction approximately equal to the scan spacing and the dimension along the scan direction somewhat smaller.
The shortcoming of the above system is that the natural spot profile for a laser beam is a circularly symmetrical Gaussian shape. By placing an aperture in the system, part of the Gaussian beam is cut off so that there is a light loss and hence a reduction in the efficiency of the system. In addition, diffraction problems arise from introducing an edge (of the aperture) into the beam resulting in (a) a reduction in the depth of focusing of the system and/or (b) ringing at the outer edges of the spot image. Further, adjustments to such systems require skilled technicians capable of diagnosing, measuring and varying the optics of the system.
In view of the above, it is the principal object of the present invention to provide a method of scanning for receiving and transmitting in facsimile equipment wherein the natural spot profile for a laser beam is utilized. A further object is to provide such a method wherein the circular beam is utilized to provide an elongated spot profile covering substantially the entire height of a scan line so that the reproduced image is virtually free of scan lines. A still further object is to provide a method wherein adjustments may be made electronically and withot requiring any optical adjustments.